1. Field of the Invention
This invention relates generally to a novel apparatus and process for mixing and dispensing high viscosity, multiple component, reactive liquids, and more particularly, to a novel apparatus and process useful in molding a high viscosity, multiple component, reactive fireproofing material onto the surface of equipment, such as electric valve actuators.
2. Prior Art
In petroleum refineries and petrochemical plants, there exist enormous amounts of flammable products being stored, pumped, and processed. These flammable products represent a very great fire hazard to all equipment where such flammable products might be present. The release of flammable products in a refinery or chemical plant can result in enormous fire damage to the plant if such flammable material is ignited. The release of flammable material can result from the failure of a mechanical seal on a pump, the rupture of piping, the failure or leaking of a process valve, or a large number of other possible causes.
One of the primary methods in preventing large fires and in stopping them once they have started is to control the release of flammable product into the area where the fire is burning. The prevention or control of such a fire depends greatly upon cesstion of the flow of flammable product before serious and irreversible damage can be done. Once the flammable product is no longer available, the fire can be easily extinguished.
In order to stop the flow of flammable products under such circumstances, many refineries and chemical plants provide isolation or block valves to shut off the flow of flammable product so that the fire can be easily extinguished. These isolation or block valves are often remote-controlled motor operated valves. In terms of sensitivity of fire, it is usually the case that the valve actuators and related control equipment are more troublesome than are the valves themselves. Typically, the valves themselves used in this environment have heavy steel castings and machined parts so that they are not affected by a fire to the extent that they require protection themselves. Heat sensitive equipment in these emergency shutdown systems include valve actuators, junction boxes, disconnect switches, and wiring conduit and conduit fittings.
As an example of heat sensitive equipment, actuators of the electromechanical type usually include soft metal, plastic parts, and sensitive electrical components that require protection from fire so that the actuator can be relied upon to activate the valve when needed, even when the valve itself is directly in the fire. Typical of the type of electromachanical valve actuator used in this environment are those sold under the Series 2000 designation by E.I.M. Company, Inc. of Missouri City, Tex.
One solution to protecting equipment such as valve actuators and junction boxes under extremely high temperature conditions is shown in U.S. Pat. No. 4,413,683, which discloses a fireproof enclosure made of a ceramic fiber material in a vacuum molding process. The fireproof enclosure is placed around the actuator to be protected. Such enclosures, however, do not permit easy access to the enclosed equipment for routine maintenance. Further, in some cases, there may not be adequate room to mount such enclosures.
Wiring conduit and conduit fittings have been protected using a ceramic fiber blanket wrapped around the conduit. Molded calcium silicate pieces have also been placed over conduit for fire protection. These methods, however, require significant labor in the plant for installation.
More recently, an alternative system has been developed for protecting emergency shutdown equipment in extreme high temperature conditions which involves the application of an intumescent fireproofing material directly to the equipment to be protected. One such intumescent coating material is sold by Avco Corporation, Lowell, Mass. under the trademark CHARTEK.RTM., including two grades, a more viscous grade designated 59 and another grade designated 59-C. CHARTEK.RTM. intumescent fireproofing is supplied as a two component system, a liquid resin and a liquid hardener. Both components are highly viscous. For the CHARTEK.RTM. 59-C grade of fireproofing, for example, the resin has a viscosity of about 58,000 centipoise at about 115.degree. F. and the hardener has a viscosity of about 4300 centipoise as measured on the Brookfield scale. According to the information known to applicant, CHARTEK is a two component polyamide cured, epoxy coating including a resin filled with encapsulated micadust, fibrous glass and bisphenol (a Diglycidyl Ether). The hardener contains flame retardant chemicals such as triethylene tetramine and diethylene triamine.
The resulting fireproofing material has a viscosity of about 20,000 centipoise. CHARTEK.RTM. fireproofing material has been used by spray applying the mixed components to the surface of the object to be protected, such as structural steel members used in various industrial applications.
Initially, the process of using intumescent fireproofing on equipment such as valve actuators, junction boxes, breaker boxes, conduits, etc., involved hand mixing the components and hand applying the material to the outer surface of the equipment. For adequate protection of the equipment, CHARTEK.RTM. 59 fireproofing material is hand applied to a thickness of about one-half inch over the equipment surface. This thickness is recommended by Avco Corporation to meet the fireproofing specifications of the major oil companies. In testing, the hand-applied CHARTEK.RTM. 59 intumescent coating protected valve actuators in fire conditions of over 2000.degree. F. such that the interior of the actuators experienced temperature rises in the range of about 72.degree.-110.degree. F. over an exposure period of 25 minutes. Major oil company specifications require a temperature rise of 200.degree. F. maximum for a 20 minute exposure to fire conditions.
However, this manual process of applying the fireproofing material has two drawbacks. First, hand mixing the two components can introduce voids into the fireproofing material, which reduces the fireproofing effectiveness of the coating on the equipment, and the components may be inadequately mixed or mixed at an improper ratio. Second, applying the material by hand to equipment is labor intensive and results in a somewhat unattractive product. Smooth, even surfaces are difficult to achieve in a hand application method.
It has been found that an attractive intumescent coating fireproofed product can be achieved by molding the CHARTEK.RTM. 59-C fireproofing material onto a piece of equipment or component parts of a piece of equipment. This can be accomplished by producing a mold that follows the general contours of the part while allowing a one-half inch thickness of fireproofing to be cast around the part, placing the part in the mold with a one-half inch space between the mold and the part, and introducing the fireproofing material into the space between the mold and the part. Simple equipment, such as conduits, can be molded completely in a single mold. For more complex equipment, such as valve actuators, component parts are not detrimental to the protection of the equipment because the intumescent fireproofing material intumesces or expands to 3 to 4 times its original size when exposed to flame, covering up any seams.
However, because of the shape and size of the pieces of equipment to be coated, it is extremely difficult to introduce the fireproofing material into the mold and assure that the mold is properly filled without air voids. Introducing the material from the top of the mold by hand may generate air voids, because CHARTEK.RTM. 59-C intumescent fireproofing in such a highly viscous material. It is desirable to introduce the viscous intumescent coating at the bottom of the mold to minimize the development of air voids.
Equipment exists for the mixing and dispensing of reactive components. However, none of these existing systems are suitable for mixing and dispensing the highly viscous intumescent fireproofing material discussed here. One system used in molding boots is shown in U.S. Pat. No. 4,037,758 to Bourque, in which components such as a prepolymer and a curative are delivered by positive displacement pumps through a special valve, through a static mixing tube, and out a dispensing valve. However, the complexity of the material flow path and flow restrictions in this system are inappropriate for handling the high viscosity materials contemplated by the present invention. It appears that the special valve incorporated into this system with its elastic diaphragms could not operate on a highly viscous material such as CHARTEK.RTM. 59-C fireproofing. Nor does it appear that this system could provide sufficient pressure to such highly viscous materials before the material enters the positive displacement pumps used in the system.
U.S. Pat. No. 4,1701,319 to Suh et al. shows a system in which two liquid components are stored in accumulators at preselected pressures and are supplied to a mixing device through mechanically linked positive displacement pumps. The patent mentions materials having viscosities in the range from 10-1000 centipoise. It appears that this system would not be capable of handling materials having viscosities in the range of 4300 centipoise or 58,000 centipoise. Particularly, it does not appear that the bladders in the accumulators used in this system could handle such highly viscous materials.
Systems are commercially available and used for separately mixing and then spray applying CHARTEK.RTM. 59 fireproofing material. However, these spray systems develop extremely high pressures in the material by use of piston type positive displacement pumps, making them inappropriate for use in dispensing the fireproofing material into a mold.